The present invention relates to high efficiency amplifiers, and it relates, more particularly, to push-pull amplifiers employing different transistors having similar characteristics in terms of biasing and signal operation.
Conventional push-pull, amplifiers include two identical signal branches that operate in 180 .degree. phase relationship or in phase opposition wherein input and output connections are each balanced to ground. The phase relationship produces additive output components of the desired wave. A disadvantage is that the passive circuit elements required to establish the phase relationship between the two branches occasion losses particularly in the output portion of the amplifier. These losses are present no matter what class of operation, for example, class A mode or class B mode, is used for the active amplifying devices.
In high frequency amplifiers, GaAs FETs are generally employed in the push-pull configuration which operates in a class B mode. Typically, a 180 .degree. balun is used on the input side of the amplifier while a 180 .degree. combiner is used on the output side of the amplifier. Both of these components introduce additional losses and restrict the bandwidth of operation by narrowing it. The overall efficiency of push-pull amplifiers currently available is similar to a class A amplifier due to the additional losses in the balun and combiner.